The ocular motor sybsystems have been studied quantitatively in patients with congenital nystagmus. Eye movements have been recorded by electro-oculography and functions of the saccadic pursuit, optokinetic and vestibulo-ocular subsystems have been analyzed with a laboratory computer. Preliminary results indicate that the saccadic subsystem is normal, except for slight to moderate abnormalities in initiation and accuracy of saccades. The gains of the pursuit and optokinetic sybsystems have been abnormally decreased in most patients studied thus far. In contrast, the gains of the vestibulo-ocular subsystem during rotation in the dark have been normal or slightly increased in all patients. Simultaneous stimulation of the optokinetic and vestibulo-ocular subsystems have demonstrated abnormal interactions of these subsystems due to impaired optokinetic responses.